Process for thermal decomposition of sulfuric acid sludges



PRDCESS FOR THERMAL DECOMPOSITION OF SULFURIC ACID SLUDGES Hunter Mileyand Henry Sonneborn III, Petrolia, Pa., Gustave Schindler, Sands Point,N.Y., and Ferdinand W. Breth, Peta-cilia, Pa., assignors to L. SonnebornSons, inc., a corporation of Delaware No Drawing. Application February6, 1956 Serial No. 563,430

8 Claims. (Cl. 23-177) This application is a new and useful process forthe thermal decomposition of sulfuric acid sludges.

Sulfuric acid is used in the treatment of hydrocarbons and hydrocarbondistillates for a variety of purposes. Concentrated sulfuric acid isused to react with and remove undesirable components of petroleumhydrocarbons and hydrocarbon distillates, ranging from residua, heavylubricating oils, kerosenes, naphthas and gasolines. Filming sulfuricacid and sulfuric anhydride are used in the treatment of such petroleumdistillates to remove all components other than naphthenes and paraflinsin the production of so-called white oils, transformer oils, odorlesskerosenes and distillates of lower boiling range. Sulfuric acid of about98% concentration is used at around C. as a cyclic reaction catalyst tocatalyze the coupling of paraffins to unsaturates. This is technicallyknown as alkylation. In each of the above cases the sulfuric acid entersinto combination with an unsaturated hydrocarbon component to form acompound that is relatively insoluble in the residual treatedhydrocarbon and may therefore be separately recovered. These sulnitedStates Patent furic acid compounds are generically referred to assludges and those resulting from the alkylation reaction are referred toas alkylation sludges.

Inasmuch as the sludges per se are of little economic value, it isimportant to recover the sulfur dioxide values, leaving a residue. Asdisclosed in the co-pending application of Hunter Miley, Serial No.538,988, filed October 6, 1955, each particular sludge has a temperatureof decomposition at which it is resolved into sulfur dioxide and aresidue which is essentially a coke although still containing somevolatile constituents. These decomposition temperatures lie within thegeneral range of from 350-600" F. If the sludge is heated to atemperature which does not exceed this decomposition temperature by morethan 50 F. the sulfur is selectively liberated in the form of sulfurdioxide contaminated with only relatively small amounts of hydrocarbonvapors. After subjecting the sulfur-dioxide containing gas to oxidation,with added air to convert the hydrocarbon vapors into carbon dioxide andwater vapor, the sulfur dioxide may be reco'nverted to sulfuric acid bythe contact process. Even with those sludges which have a relativelyhigher temperature of decomposition within the range specified, it isevident that the final temperature of thermal decomposition should notexceed 650 F.

One method of accomplishing this decomposition is to admix the sludgewith a stream of coke particles moving continuously in a closed cycle,with the sludge particles heated to a predetermined temperature not over50 F. in excess of the decomposition temperature of the particularsludge, and in amount sufiicient to supply the heat required to elevateall of the sludge introduced to at least the decomposition temperature.This splits off the sulfur dioxide with only a very few percent ofhydrocarbons in the gas phase, leaving a dry, granular residue whichadds to the coke particles in the stream. The

efiiuent gases are conducted away, admixed with air and burned toconvert the hydrocarbons into carbon dioxide and water vapor, followingwhich the gas so produced is returned to the sulfuric acid generator.

The coke particles move in a continuous cycle and, following removal ofthe sulfur clio'xide, are again heated to the predetermined temperatureand recycled to the point at which the sludge is admixed with the cokeparticles. The excess of coke which is continuously produced bydecomposition of the sludge is continuously removed from the system.

The process and the apparatus in which the process is carried out aredescribed in detail in said co-pending application, Serial No. 538,988.Another process in which the sludge may be decomposed by heating withincontrolled limits is described in U.S. Patent No. 2,395,- 503. This alsoutilizes a stream of coke particles moving continuously in a closedcycle, but in this case the wire at the point of mixing with the sludgeis below the temperature of decomposition of the sludge and the heatnecessary to effect the decomposition is thereafter introduced byindirectly heating the mixture.

One limitation on each of the processes described is that they do notoperate to best advantage with those sludges in which the titratableacidity of the sludge, assumed as H SO or more. In these casesdecomposition under the conditions recited is incomplete andundecomposed sludge builds up in the system to eventually interfere withthe free movement of the stream of solid particles and/or cause freesulfuric acid to vaporize. One sludge which is particularly difiicult toprocess in systems of the type described is the so-called alkylationsludge, which is a residue from the use of concentrated sulfuric acid asa cyclic reaction catalyst in the coupling of olefins with paraflins tointroduce an alkyl radical as side chain.

We have found, however, that such sludges of a titratable acidity of atleast 75% can be processed continuously in systems of the typedescribed, with substantially com plete decomposition of the acid andthe production of a free-flowing granular coke residue, if prior to themixing of the sludge with the coke particles the sludge is commingledwith a relatively small amount of a heavy hydrocarbon oil. The oilsreferred to are those which do not have more than a few percent boilingbelow 500 F. and preferably not more than a few percent boiling below700 F. The mixing is preferably carried out continuously immediatelyprior to the introduction of the sludge to the decomposer. This may bedone in any suitable type of mixer adapted to commingle two liquidphases. The amount of the oil may vary within the limits of from 2-15%by weight in relation to the sludge, the larger amounts being requiredfor those sludges with higher titratable acidity. Even relatively smallamounts will sufiice with those sludges of lower titratable acidity toeliminate completely the operating difiiculties otherwise encounteredwith such sludges.

Example 1 As a practical example of the operation of our process analkylation sludge which, on titration, analyzed 87.8% H 50 could not besuccessfully processed in the apparatus and in accordance with theprocess described in aid co-pending application, Serial No. 538,988.

This was commingled with 5% of a bunker C fuel oil having an initialboiling point of about 700 F. The mixture of alkylation sludge and oilwas processed with entire success in the process and apparatus describedin said co-pending application, with the production of a dry, granularcoke residue. The top temperature of the mixture was 600 F. and theyield of S0 corresponded oil referred to in the preceding example. ofalkylation sludge and oil was processed with success in the process andapparatus described in said co-pending c 3 V to- 89.5% of thesulfuricaeid content of the'sludge as determined by titration. e

Example 2 Asafurtherpractical example of the application of our process,an alkylation sludge which, ontitration, analyzed 85;2% H 'SO could notbe successfully processed in apparatus and in accordance with theprocess described in said .c'o-pending application, Serial No. 538,-988. This was intimately mixed with of the same The mixture application.The coke was granular but not completely dry and brittle. The yield ofsulfur dioxide corresponded 'to' 76.4% of the sulfuric acid content ofthe sludge as determined by titration. i

Example, 3

Asa further practical example of the application of our process analkylation sludge which, on titration, analyzed 87.8% H 80 could not besuccessfully processed in. apparatus and in accordance with the processdescribed in said co-pendingapplication, Serial No. 538,- 988.' This wasintimately mixed with 10% o'f'the same oil referred to in the precedingexample.

The mixture of alkylation sludge and oil was processed with entiresuccess in the process-and apparatus described in said co-pendingapplication, with the production ofa dry,'brittle, granular cokeresidue. The top' gas consisting substantiallyexclusively of sulfurdioxide,

the improvement which comprises admixing a hydrocarbon oil substantiallyfree'fromcompo'nents boiling below 500 F. with said sludge prior toadmixing the same with saidlstream of coke particles, said hydrocarbonoil being added in an amount 'sufficient to produce a dry granular cokeas the residue of the process.

2. Process according to claim 1 in which the amount of oil admixedranges from 245% by weight of said sludge.

' 3.111 the decomposition of sulfuric acid alkylation sludges derivedfrom the treatment of hydrocarbons with sulfuric acid and containingtitratablc acidity equivalent to atleast 75% calculated as H 80 byadmixing the same with a stream of coke particles moving in a closedcycle, thereby forming a mixture, subjecting said mixture totemperatures at which said sludge is selectively decomposed with theproduction of a'coke residue and a gas consisting substantiallyexclusively. of sulfur dioxide, the improvement which comprises admixinga hydrocarbon o'il substantially free from components boiling below 700F. with said sludgeprior to admixing the same with said stream of cokeparticles, said hydrocarbon oil being added in an amount sufiicient toproduce a dry granular coke as the residue of the process.

4. Process according to claim 3 in which the amount or oil admixedranges from 245% by weight of said sludge. i

5. In the decomposition of sulfuric acid alkylation sludges derived fromthe treatment of hydrocarbons with sulfuric acid and containingtitratable acidity equivalent to at least 75%. calculated as H SO byadmixing the same with'a stream of coke particles moving in a closedcycle, thereby forming a'mixture, subjecting said mixture totemperatures notexceeding' 650 F. at which said sludge is selectivelydecomposed with the p roductioncf a coke residue-and a gas consistingsubstantially exclusively of sulfur dioxide, the improvement whichcomprisesadmixing a hydrocarbon oil substantially free from componentsboiling below'5 00" Frwith said sludge prior to admixing the same withsaid stream of coke particles,

said hydrocarbon oil being added in an amount sufiicient to produce adry granular coke as the residue of the process.

' oil substantially free 6. Process according to claim 5 in which theramount of oil admixed ranges from 2-15% by weight of said sludge. i a a7. In the decomposition of sulfuric'acid alkylation sludges derived fromthe treatment of hydrocarbon with sulfuric acid, and containingtitratable acid equivalent to to at least %'calculated as H by admixingthe same with a stream ofpreheated coke particles moving in aclos edcycle, thereby forming a mixture at a temperature at which the sludge isselectively decomposed with the production of a coke residue and a gasconsisting substantially"exclusively of sulfur dioxide, the improvementwhich comprises admixing a hydrocarbon from components boiling below 700F. with said sludge prior to admixing the same with said streamoficokepartic'les, said hydrocarbon oil being coke as the residue of theprocess;

8. Process according to claim 7 in which the amount of oil admixedrangesfrom 2 to 15% by weight of said sludge. i}

References Cited in the file of this patent UNITED STATES PATENTS

1. IN THE DECOMPOSITION OF SULFURIC ACID AKYLATION SLUDGES DERIVED FROMTHE TREATMENT OF HYDROCARBONS WITH SULFURIC ACID AND CONTAININGTITRATABLE ACIDITY EQUIVALENT TO AT LEAST 75% CALCULATED AS H2SO4 BYADMIXING THE SAME WITH A STREAM OF COKE PARTICLES MOVING IN A CLOSEDCYCLE, THEREBY FORMING A MIXTURE, SUBJECTING SAID MIXTURE TOTEMPERATURES AT WHICH SAID SLUDGE IS SELECTIVELY DECOMPOSED WITH THEPRODUCTION OF A COKE RESIDUE AND A GAS CONSISTING SUBSTIANTILLYEXCLUSIVELY OF SULFUR DIOXIDE, THE IMPROVEMENT WHICH COMPRISES ADMIXINGA HYDROCARBON OIL SUBSTANTIALLY FREE FROM COMPONENTS BOILING BELOW500*F. WITH SAID SLUDGE PRIOR TO ADMIXING THE SAME WITH SAID STREAM OFCOKE PARTICLES, SAID HYDROCARBON OIL BEING ADDED IN AN AMOUNT SUFFICIENTTO PRODUCE A DRY GRANULAR COKE AS THE RESIDUE OF THE PROCESS.